The White M Hairstreak (Parrhasius m-album) is a southeastern hairstreak with a distinctly marked hindwing and beautiful top wing.
The White M is a medium size butterfly, but would probably be considered large for a hairstreak. It is not very common in Maryland, as far as I can tell, but the hairstreaks are tough to identify with the naked eye, so I may have seen more than I think.
The one above was photographed at Idylwild WMA.
The upperside of the White M is a glorious blue, visible only in flight as the White M sits with wings closed. Still, with wings closed it is easy to distinguish with a single white speck at mid-wing and the single strong red spot.